The present invention relates, in general, to semiconductor devices, and more particularly, to a novel method of manufacturing a vertical current flow semiconductor device.
In recent years, a class of power semiconductor devices typically referred to as an insulated gate bipolar transistor (IGBT) had been developed by the semiconductor industry. Of particular interest had been an enhanced insulated gate bipolar transistor (EIGBT).
Previous methods for creating enhanced insulating gate bipolar transistors (EIGBTs) typically involved forming a series of P and N regions in a checkerboard pattern on one surface of a semiconductor wafer, growing an epitaxial layer to cover the P and N regions, and diffusing a field effect transistor structure in the epitaxial region above the P and N areas. The EIGBT's drain electrode was a conductor that electrically connected the P and N regions. The drain electrode was created by first removing material from the wafer surface opposite the P and N regions until the P and N regions were exposed. Then the drain electrode was formed by covering the exposed P and N regions with a conductor. Because a large amount of material had to be removed from the wafer before the P and N regions were exposed, the resulting wafer typically had a thickness of approximately 100 to 130 microns. Such thin wafers were difficult to handle in a wafer processing area and resulted in a high incidence of wafer breakage thereby increasing the EIGBT's cost. To ensure that the removal procedures did not inadvertently obliterate the P and N regions, the regions typically were formed with a thickness of approximately 50 microns. Formation of such deeply diffused regions required diffusing at temperatures of approximately 1250 degrees centigrade for approximately 50 hours which resulted in a high manufacturing cost. Additionally, the removal operations utilized to expose the P and N regions had wide tolerances that resulted in non-uniform thickness of the P and N areas. The P and N thickness variations resulted in EIGBTs that had widely varying operating characteristics such as source-drain voltage drop, maximum drain current, and turn-off time.
Accordingly, it is desirable to have a method for producing EIGBTs that uses thick wafers that are easy to handle, that has a low manufacturing cost, and that results in EIGBTs with consistent operating characteristics.